Method of preparing adipic acid esters



United States Patent U.S. Cl. 204-158 7 Claims ABSTRACT OF THE DISCLOSURE In the method of preparing adipic acid esters by the reductive dimerization of acrylic acid esters, the improvement which comprises subjecting to exposure of actinic light a mixture consisting of an acrylic acid ester, an iron corbonyl compound and compounds selected from the group consisting of water, alcohols and phenols.

This invention relates to a method of preparing adipic acid esters.

An electrochemical method has heretofore been known as means of preparing the adipic acid esters by dimerizing acrylic acid esters. For instance an adipic acid ester is obtained by using mercury as cathode and a quaternary ammonium salt as supporting electrolyte and electrolys ing ethyl acrylate (J. Electrochem. Soc. 111, 223, (1964) However, there are various difficulties in carrying out the electrolysis of organic compounds industrially. For instance, in the case of the electrolysis of acrylic acid esters, substance usable as supporting electrolyte are limited owing to considerably high reduction voltage of the acrylic acid esters. Further, as a specific resistance of the electrolytic solution is great, the distance between electrodes must be made narrow, with the consequence that an electrolytic cell of a complicated structure should inevitably be used. Still further, as the use of a specific diaphragm such as an ion-exchange membrane is inevitable, it is one of difficulties that such specific diaphragm is very brittle and expensive.

Another known method is a so-called amalgam method 7 which comprises electrolysing a potassium compound to prepare potassium-mercury amalgam, dimerizing acrylic acid esters reductively by using a combination of the said amalgam and an acidic substance, and thereby obtaining adipic acid esters. According to this method, the yield of adipic acid esters is as low as about 50% (ibido.).

On the other hand, the present invention is to provide a method for the photochemical reductive dimerization of acrylic acid esters in high yields, which can be industrially carried out by using a simple apparatus.

We found that the adipic acid esters could be prepared in good yield without the formation of a substantial amount of by-products by a method consisting of subjecting a mixture of an acrylic acid ester, an iron carbonyl compound and at least one hydroxy compound selected from the group consisting of water, alcohol and phenols to exposure of actinic light, followed, if desired, by further heating of the mixture. Thus, according .to this invention, a method is provided wherein by the reductive dimerization of the acrylic acid esters, adipic acid esters corresponding to the dimers of the acrylic acid esters are formed, the method being characterized in that a mixture of an acrylic acid ester, an iron carbonyl com- 3,491,005 Patented Jan. 20, 1970 pound, and a compound of the group consisting of water, rlalcghols and phenols is subjected to exposure of actinic The various acrylic acid esters which are commercially available can be used in this invention. Suitable acrylic acid esters include the alkyl esters of 1 to 12 carbon atoms and cycloalkyl esters of 3 to 12 carbon atoms of acrylic acid. These acrylic acid esters are exemplified by methyl, ethyl, nor iso-propyl, nisoor sec-butyl, nor iso-amyl, n-hexyl, n-octyl, n-nonyl, n-decyl, lauryl, or cyclohexyl acrylate. Of these acrylic acid esters, particularly to be preferred are those containing alkyl of 1-3 carbon atoms, since the distillation of the adipic acid esters formed therefrom are readily carried out.

As the iron carbonyl compounds, various classes of those which are known can be used. Of the known iron carbonyl compounds, those which are conveniently usable include Fe(CO) Fe (CO) Fe (CO) H Fe(CO) and C H N(CO) Fe(CO) is easily handled and hence is the most suitable iron carbonyl compound for this invention. While there is much latitude as to the amount.

in which these iron carbonyl compounds can be added to the acrylic acid esters, generally speaking, the addition of from 0.01 to 1 mole, and particularly from 0.02 to 0.3 mole of iron carbonyl per mole of acrylate, is prea ferred for exhancernent of the yield of the adipic acid esters.

Inthis invention, a hydroxy compound of the group consisting of water, alcohols and phenols is mixed with the aforesaid acrylic acid esters and iron carbonyl compounds, following which the mixture is subjected to exposure of actinic light. A monohydr-ic alcohol of 1-12 carbon atoms is preferably used in this invention. Usable are, for example, the primary, secondary and tertiary aliphatic saturated alcohols such as methanol, ethanol, nor iso-propanol and n-, iso-, sec.- or tert.-butanol; the hols such as allyl alcoho, crotyl alcohol and cyclohexa-nol. 'icyclododecanol; the aryl-subtszt-ituted alcohols such as benzyl alcohol; and acrylic and cyclic unsaturated alcohols such as allyl alcohol, crotyl alcohol and cycohexanol. Further, not only the aforesaid monohydric alcohols but .also the polyhydric alcohols of 2-12 carbon atoms, such .as ethylene glycol, propylene glycol, 1,6-hexanediol, 1,2- cyclohexanediol, 1,4-cyclohexanedoil, glycerine and pentaerythritol, can also be used in the invention. Needless to say, the foregoing alcohols can be used in combination.

Examples of the phenols to be used in this invention i3I6 phenol, o-cresol, m-cresol, p'cre'sol, a-naphthol, ,B-naphthol, hydroquinone, pyrocatechol, resorcin, pyrogallol, 1,2-naphthalenediol, 1,4-naphthalenediol and 9,10- anthracenediol.

Not only can water or the aforementioned alcohols or phenols be used alone in this invention, but it is also possible to use two or three of them in combination. The hydroxy compound should be used in a 'suflicient quantity. It is preferable to use it in an amount sufficient to give at least 0.5 mole equivalent of OH group per mole of an iron carbonyl compound.

The actinic light to which the mixture of acrylic acid esters, iron carbonyl compounds and water or alcohols or phenols is exposed can be light from any light source. The light source used include such, for example, as a high pressure mercury lamp, ultrahigh pressure mercury lamp,

low pressure mercury lamp, fluorescent lamp and xenon lamp. The exposure to light is preferably carried out in an atmosphere of either nitrogen, argon, carbon monoxide, carbon dioxide or hydrogen. The exposure to light can generally be carried out at a temperature ranging from ambient temperature to 150 C. While the period of exposure will vary depending upon such as the output of the light source, the temperature during the exposure and the amount of the reactants, this can be readily determined by those skilled in the art for obtaining a substantial conversion of the acrylic acid esters to the adipic acid esters.

While the reaction proceeds at room temperature, it is accelerated upon raising the temperature. Thus, the reaction is accelerated, if heating is carried out concurrently with the exposure of the reaction mixture to light. Again, the yield of the adipic acid esters can also be enhanced by heating the reaction mixture after switching off the light after exposure of the mixture at below room temperature. This method is especially recommended, since the hindrance to the transmission of light owing to soiling of the reactor wall is less in this case. When the latter method is to be practiced, it is generally preferable to carry out the heating after exposure of the reaction mixture to light for 0.1 to 10 hours at a temperature ranging from 40 C. to 200 C.

In carrying out the exposure to light or post heating of the mixture of an acrylic acid ester, iron carbonyl compound and either water, alcohols or phenols, the addition of a small amount of a known polymerization inhibitor such as hydroquinone is desirable for restraining the polymerization of the acrylic acid ester. Further, an inert solvent such as acetonitrile, propionitrile and ethyl acetate can be added to the material mixture.

The recovery of the adipic acid ester from the reaction mixture can be readily carried out by distillation in a manner known per se.

According to the invention method, adipic acid esters can be obtained in good yield of as high as 75 to 90% from acrylic acid esters by the combination of the exposure to actinic light and the use of iron carbonyl compounds and either water, alcohols or phenols. The resulting yield is considerably greater than that obtained by the conventional method of preparing adipic acid esters by means of the reductive dimerization of acrylic acid esters.

For a better understanding of the invention, the following nonlimitative examples are given, wherein the parts, unless otherwise indicated, are on a weight basis.

EXAMPLES 1-3 A mixture consisting of 96 parts of one acrylic acid ester shown in the table below, 10 parts of iron pentacarbonyl and 4.0 parts of water was exposed for 3 hours at room temperature to light from a high pressure mercury lamp in an atmosphere of nitrogen. Thereafter, the mixture was transferred to a nitrogen-purged pressure reactor where the mixture was heated to 110 C. for 5 hours. The rate of conversion of the acrylic acid ester to an adipic acid ester and the yield of the adipic acid ester based on the reacted acrylic acid ester are shown in the table below.

A mixture consisting of 95 parts of one acrylic acid ester shown in the table below, 15 parts of iron pentacarbonyl and one hydrogen donor in an amount shown in the table below, was exposed at room temperature for 2 hours to light from a high pressure mercury lamp in an atmosphere of nitrogen. Thereafter, the mixture was transferred to a nitrogen-purged pressure reactor where the mixture was heated to 110 C. for four hours. The rate of conversion of the acrylic acid ester to an adipic acid ester and the yield of the adipic acid ester based on the reacted acrylic acid ester are shown in the table below.

Conversion Yield No. Esters Hydrogen donors (percent) (percent) 4 Methyl ester Methanol (16 parts)..- 8. O 5 do opropanol (16 parts) 12. 0 75 6. Ethyl ester Ethanol (16 parts) 10.0 7-. do Isopropanol (16 parts). 7.0 88 8-. Methyl ester Phenol (28 parts) 7. 5 85 o Hydroquinone (8.2 6. 3 78 parts). 10 Ethyl ester.. Hydroquinone (8.2 6.4 76

parts). 11 Methyl ester- Ethylene glycol (16 5. 4 82 pa s 12 do B-naphthol (21 parts) 6. 9 7 4 EXAMPLES 13-15 A mixture consisting of parts of ethyl acrylate, 14 parts of iron pentacarbonyl and 2. parts of water was exposed for 3 hours to light from a high pressure mercury lamp at the temperature shown in the table below. The rate of conversion of the acrylic acid ester to the adipic acid ester and the yield of the adipic acid ester based on the reacted acrylic acid ester are shown in the table below.

Temperature Conversion No. 0.) (percent) Yield (percent) EXAMPLE 16 EJQAMPLE 17 A mixture consisting of 95 parts of methyl acrylate, 15 parts of iron pentacarbonyl, 8.2 parts of hydroquinone and 16 parts of methanol was subjected to exposure of actinic light and a heating treatment in the same manner as in Example 4. As a result, the rate of conversion of methyl acrylate to dimethyl adipate was 7.3% and the yield of dimethyl adipate based on the reacted methyl acrylate was 78%.

EXAMPLE 18 A mixture consisting of 95 parts of methyl acrylate, 15 parts of iron pentacarbonyl, 10 parts of methanol and 4.0 parts of Water was subjected to exposure of actinic light and a heat treatment in the same manner as in Example 4. As a result, the rate of conversion of methyl acrylate to dimethyl adipate was 6.7% and the yield of dimethyl adipate based on the reacted methyl acrylate was 89%.

We claim:

1. In the method of preparing adipic acid esters by the reductive dimerization of acrylic acid esters, the improvement which comprises subjecting to exposure of actinic light a mixture consisting of an acrylic acid ester, an iron carbonyl compound and compounds selected from the group consisting of water, alcohols and phenols.

2. The method according to claim 1 wherein said acrylic acid ester is a lower alkyl acrylate.

3. The method according to claim 1 wherein said iron carbonyl compound is Fe(CO) 4. The method according to claim 1 wherein said alcohol is a monohydric alcohol of from 1 to 4 carbon atoms 5. The method according to claim 1 wherein said phenol is hydroquinone.

6. The method according to claim 1 wherein the exposure to actinic light is carried out at a temperature ranging from ambient temperature to 150 C.

7. In the method of preparing adipic acid esters by the reductive dimerization of acrylic acid esters, the im- 10 provement which comprises subjecting to exposure of actinic light a mixture consisting of an acrylic acid References Cited UNITED STATES PATENTS 3,203,886 8/1965 Griflin 204-158 HOWARD S. WILLIAMS, Primary Examiner 5/1968 Anello et al. 204-158 XR UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,491,005 January 20, 197

Shigeru Wakamatsu et a1.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 50, "(ibido.)" should read (ibid) Column 2, line 41, "hols such as allyl alcoho, crotyl alcohol cyclohexanol" should read alicyclic alcohols such as cyclohexanol, cyclooctanol and line 44, "cycohexanol" shou read cyclohexanol Column 4, line 22, "2." should read Signed and sealed this 17th day of November 1970.

(SEAL) Attest: 7

Edward M. Fletcher, Jr. WILLIAM E. SCHUYLER,

Attesting Officer Commissioner of Pater 

